1. Field of the Invention
The present invention relates generally to outboard engine units, and more particularly an improved air intake structure for introducing air into a unit""s interior defined by an engine cover.
2. Related Prior Art
Generally, outboard engine units include an engine, an exhaust system and a propellor shaft extending below the engine, and a propellor device (screw) disposed rearward of a gearbox connected to the lower end of the propellor shaft. As viewed from the outside (i.e., in outer appearance), the outboard engine units include an engine cover at the top, an extension case located below the engine cover, and the gearbox and the like at the bottom. To secure a supply of air for combustion of an air/fuel mixture in the engine, there is a need to introduce air into the engine unit""s interior defined by the engine cover.
One example of an air intake structure for introducing air into the unit""s interior defined by the engine cover is proposed by the assignee of the instant application in Japanese Patent Laid-open Publication No. HEI-4-166496 (U.S. Pat. No. 5,445,547). The proposed air intake structure includes a rib formed on and protruding inwardly from the inner surface of the engine cover made of resin, and a channel-shaped guide member also made of resin and jointed face to face to the rib so that an air intake guide is provided by the inner surface of the engine cover and the guide member.
The proposed air introducing structure, however, would present the following inconvenience. First, it is very difficult to ensure airtightness or sealability between the jointed surfaces of the rib and the guide member. Second, it is very difficult to join the resin-made guide member to the resin-made engine cover with high accuracy. Further, in the air intake structure, the sealing surfaces extend continuously from the inner surface of the top portion of the engine cover to the inner surface of the sides of the engine cover; namely, the sealing surfaces do not lie in one and the same plane, which would also make it difficult to join the guide member to the engine cover with high accuracy.
Furthermore, the engine cover, which constitutes an outer shell member of the outboard engine unit, is subject to deformation due to application thereto of external force and vibration caused by vibration of the engine in operation. Therefore, even severer requirements must be met with regard to the joint between the inner surface of the engine cover and the guide member. Sealing deficiency in the jointed surfaces of the engine cover and the guide member would lead to undesired scattering or spray of water by a negative pressure of intake air.
It is accordingly an object of the present invention to provide an improved outboard engine unit which includes an air intake guide disposed within an engine cover independently of the engine cover and thereby can secure highly reliable surface sealability even when the engine cover is subjected to external force or vibration caused by the engine in operation.
To accomplish the above-mentioned object, the present invention provides an outboard engine unit which comprises: an engine having a combustion chamber; an engine cover that covers the engine to define an engine room, the engine cover having an air intake opening; and an air intake guide disposed within the engine cover and surrounded by a wall that is provided independently of an inner surface of the engine cover, the air intake guide having one end communicating with the air intake opening of the engine cover and the other end opening into the engine room.
Because the air intake guide for introducing air into the unit""s interior defined by the engine cover is provided discretely from or independently of the engine cover, the present invention can eliminate the particular need for securing reliable sealability between the engine cover and the air intake guide. Therefore, it is no longer necessary to care so much about the sealability between the engine cover and the air intake guide, and the present invention can prevent the sealability of the air intake guide from being interfered with by external force applied to the engine cover that constitutes an outer shell member of the outboard engine unit or by vibration of the engine in operation.